Use cultural methods to underpin blackgrass control, Midlands growers urged 8 September 2016
Arable farmers will need to consider all methods to fight back against blackgrass, after poor control last season, say ProCam agronomists in the Midlands. According to ProCam agronomists Alex Miles, who advises growers in and around Nottinghamshire, and Neil Woolliscroft, who advises growers in and around Northamptonshire, blackgrass is forefront in everyone’s minds for this autumn.
Poor control in last season’s oilseed rape – a crop traditionally seen as helping to ‘clean up’ blackgrass – has exacerbated the problem, says Alex Miles, and placed even greater emphasis on cultural methods to underpin herbicide use.
“Effective cultural techniques will be vital,” stresses Mr Miles. “So use them to the best of your ability, also understanding your population of blackgrass is vital.
“The more you can delay drilling of autumn cereals, to kill off blackgrass before planting, the better. Having worked previously in practical farming, I can understand the temptation to drill at the first opportunity. But try to delay drilling winter wheat at least until early October, if not mid-October,” he adds.
Another method, says Mr Miles, is to choose crops that are more competitive against blackgrass, such as hybrid barley, or winter wheat varieties that grow outwards, rather than upwards, to help crowd out the weed.
“Also, try increasing the seed rate – if you can get a bit more crop competition it helps. And create a good seedbed. There’s a lot of reliance on soil-acting pre-emergence herbicides, so a clod-free seedbed will help pre-ems work better.
“For the worst blackgrass fields, drill them last – even if it means waiting to drill a spring crop to allow more time for blackgrass to chit and be sprayed off.”
ProCam’s Neil Woolliscroft agrees, and says long-term blackgrass control is the number one issue constraining farm profitability in his area.
“It dictates nearly everything we do on-farm,” says Mr Woolliscroft. “It’s clear the problem isn’t getting better using current methods. So this has prompted thinking outside the box.
“The first thing to do is understand why black-grass is such a successful weed, and how it has come to thrive in our farming system. It likes to germinate mostly during September and thrives in wet conditions. So the first of my suggestions are to delay sowing winter cereals until at least 15 October and to investigate soil drainage. Effective field drainage on heavy soils will always be cost effective,” he adds.
Additionally, Mr Woolliscroft says it is widely agreed that switching from a winter to a spring cereal is a reliable way of reducing black-grass whilst continuing to farm. Combined with this, there is a lot of talk about using cover crops between harvest in summer and drilling in spring, he notes.
“There’s no doubt that typical species used in cover crops can deliver short term environmental benefits with nutrients captured and soil erosion reduced,” says Mr Woolliscroft. “However, I question some other soil benefits during winter months.
“In addition, on-farm experimentations over recent summers have shown that levels of black-grass seed in soil can be so high that if a cover crop is established directly after harvest in August, it can be completely overwhelmed by the blackgrass.
“It’s therefore important to encourage the first ‘main flush’ of black-grass to grow and then destroy it. Unfortunately, by the time this is complete it can be too late in autumn for many small seeded cover crop species to get big enough for the winter.
“That said, what does seem clear is that black-grass prefers to grow alongside another species – for example, even after repeated stale seedbeds, the main black-grass germination still often emerges with the autumn-sown cereal.
“It’s not clear whether this is an allelopathic feature or because a finer seedbed is made for drilling the cereal than the stale seedbed. Accordingly, for this autumn, we’re going to investigate different techniques for depleting blackgrass prior to sowing a spring cereal – by comparing populations after conventional ploughing, after preparing a fine seedbed, and after a sacrificial wheat crop.
“We’re looking to see if the sacrificial wheat will deliver the short-term economic benefits of a cover crop, without the expense of bought in seed. We’ll apply glyphosate in late winter and establish the spring crop with as little soil movement as possible as it’s the soil movement which triggers remaining blackgrass germination,” Mr Woolliscroft concludes.